Automotive heating, ventilating air conditioning and ventilation modules (generally referred to as just air conditioning modules, or abbreviated to HVAC modules) consist basically of a hollow plastic housing within which are contained heat exchangers and various air flow directing devices. These components, in cooperation, receive, temper, and redirect the flow of forced air from an upstream blower to and through several downstream outlets within the vehicle. Various valves, generally in the form of swinging flapper doors, select the outlets to which the air ultimately exits, and these are generally referred to as mode valves. Air can exit high to the windshield in so called defrost and defog modes, or at various mid height outlets, or to lower, floor directed outlets, or both. The mid height outlets are often called "air conditioning" outlets and the floor outlets "heater" outlets, based on the temperature of the air which is generally thought to be most comfortable at those locations, although air of any temperature can be directed through any outlet.
The temperature of the air that ultimately reaches any outlet is generally determined by a so called reheat and air mix system, using the evaporator and heater in series. A so called temperature valve selects and divides the air flow through hot and/or cold sources and, again, is typically a swinging flapper door. The evaporator is the larger of the two heat exchangers, and extends across the entire width of the housing, so that all the forced air passes through it first, regardless of whether the evaporator is cold and enabled, or switched off. The heater, downstream of the evaporator, is significantly smaller, so that cooled (or, at least, unheated) air that has passed through the evaporator can be selectively passed through, or diverted around the heater.
A typical prior art HVAC module with reheat and air mix is shown in FIG. 1. The housing 10 contains a conventionally sized and located evaporator 12 and heater 14. For better analysis of the workings of the module, the interior of the housing 10 can be conceptually divided up into four quadrants, A, B, C and D, based on the space envelope that is inevitably occupied by the evaporator 12 and heater 14. The larger, upstream evaporator 12 occupies all of both the lower and upper upstream quadrants A and B. The smaller, downstream heater 14 occupies only the lower, downstream quadrant C, while leaving the upper, downstream quadrant D essentially empty. Quadrant D does provide space for the swinging motion of a temperature valve door 16, however, which determines the final air temperature by determining the degree to which air that has passed first through the upstream evaporator 12 is heated.
The degree of heating of the air flow is varied not by varying the temperature of the heater 14, which has a basically constant flow of hot engine coolant through it, but by varying the proportion of air flow over and through it. Temperature door 16, in conjunction with a baffle 18 in front of the downstream face of the heater 14, is moved so as to selectively block all air flow through, or permit all air flow through, or partially permit air flow through, the heater 14. Any air flowing through the heater 14 is then routed up the back face of heater 14 and into a mixing chamber area, generally denoted at E, which is external to the four quadrants just described. Within the mixing chamber E, any air that has passed straight through the evaporator 12 is mixed with any air that has been routed through heater 14 (as determined by the position of temperature door 16), to attain a final intermediate temperature. From the mixing chamber E, tempered air is then routed through whichever outlet or outlets the operator selects, including upper defroster outlet 20, mid level "A/C" outlet 22, or floor directed "heater" outlet 24.
While the basic reheat system just described has worked well for years, smaller cars present a need for more compact modules and housings. Swinging valve doors inevitably need a semi cylindrical volume within which to move, and are also inherently non linear in their response. That is, they tend to behave as either totally open or closed, and do not do well and providing a "partially open" condition. So called "film valves", in which a rolling belt with a central opening provides a precisely sized flow path and improved linearity of air flow, are seeing increased use as a response to the linearity issue.
Examples of film valve systems may be seen in U.S. Pat. Nos. 5,326,315 and 5,154,223. In general, however, such systems still mix the air well downstream of the heater, and well outside of the minimal space envelope that is inevitably occupied by the evaporator and heater. The space between the evaporator and heater is typically empty, and not occupied by any particular structure. In one case, a film belt is located in the space between the evaporator and heater, as seen in U.S. Pat. No. 5,162,020. Even there, however, the mixing zone is located well downstream of the heater, so the use of a film valve per se does not do much to make the overall module more compact, even if it is more precise in the determination of final air temperature.
Another recent design trend has been the attempt to save space by integrating the HVAC module into the structure of the car itself, especially by using the instrument panel, cross car structural beams, or both to provide air flow duct work. For example, in co assigned U.S. Pat. No. 5,709,601, the air ducts and HVAC module are both housed beneath the dashboard assembly. Because of the width of the HVAC module, the entire dashboard assembly is correspondingly quite wide as well. While this has potential for incorporation into larger mini vans and SUVs, it is not potentially as useful in small cars. Earlier patents, such as U.S. Pat. Nos. 4,391,465; 4,733,739; and 5,005,898 have all proposed similar designs, but have all gone abandoned for non payment of maintenance fees. Clearly, without a more compact design for the HVAC module itself, its integration and incorporation into the vehicle body structure will be limited.